[Grace-core] Obejctdraw

[James Noble]

> That's kind of overwhelming (and not very novice friendly).

which is why I pointed at the web version :-)

> We should talk about this philosophy before talking about a particular case.  

right.

The interface of Number will also be overwhelming (and not very novice friendly) assuming we get that far.
The question is whether we want to teach with a Point abstraction or not,
and it's crucial because it needs to be "baked in" to the library API.
(although, I guess we could have more than one graphics library over a base levels

Do we want people to think about an algebra of points, or to think about pairs of x and y coordinates?

>  I found the following paper:  "A Portable Graphics Library for Introductory CS" by Eric Roberts and Schwartz. 

In terms of abstractions, this library doesn't use a point abstraction, as far as I can see.
It uses x, y, width, height coordinates as some kind of number, and has a model
of retained, mutable graphics objects. The paper doesn't talk about whether those
objects are mouse-sensitive, or whether input only happens at the level of the window
(the example makes it look like it's per window)

I also came across this paper though -- Chris Piech and Eric Roberts, “Informatics education using nothing but a browser,” 
which I also put in the svn.   I don't know the C pipeline version would in a browser - 
we'd probably need a "native" JS implementation anyway.


In some ways, the most important decision we have to make - at least looking towards 
teaching in 2014 is: do we aim our limited resources to supporting the JS backend
or the C backend?   (or both?  or potentially other backends).  It's an unfortunate fact that JS & C
are sufficiently different that some things are much easier - and others much harder -
on each platform. 

James